1. Field of the Invention
This invention relates to a process for ortho-para-hydrogen (inter-) conversion.
2. Description of the Prior Art
It is well known that the hydrogen molecule exists in either of two forms; in one, the two atoms constituting the molecule combine with their nuclear spins in the same directions (ortho-hydrogen) and, in the other, their spins in opposite directions (para-hydrogen). The ratio of the two spin isomers in an equilibrium composition is obtained as a function of temperature. At 0.degree. C. or above, the hydrogen is in the form of ordinary hydrogen, consisting of 75% ortho-hydrogen and 25% para-hydrogen. With the lowering of the temperature, the hydrogen tends to contain more and more para-hydrogen until the percentage of the para content reaches 100% at the boiling point of hydrogen. The possibilities of the application of hydrogen in fuel, including the use of liquid hydrogen as a rocket fuel, are attracting growing attention. In those applications para-hydrogen is preferred because of its specific heat.
The rate at which hydrogen in a nonequilibrium state self-converts to an equilibrium state at a given temperature is nearly zero, even at room temperature. Practically it is next to impossible to obtain hydrogen of a desired equilibrium composition merely through temperature control. In order to effect the ortho-para-hydrogen conversion at a finite rate, some catalyst must be added to the system.
Known catalysts for the conversion have been limited to: precious metals, e.g., platinum, rhenium, and ruthenium, inorganic compounds, e.g., polyvalent transition metal oxides, e.g., trivalent manganese and iron in alumina, and chromina-alumina; and carbonaceous substances formed by calcining natural organic materials, e.g., bone-black and coconut char.
Recently, a group of organic complexes called "charge transfer complexes", e.g., alkali metal addition complexes of condensed aromatic ring compounds, have been found relatively effective in carrying out the ortho-para-hydrogen conversion. They are, nonetheless, not superior in conversion activity (particularly at low temperatures) to the conventional metal oxide catalysts.
We previously found that a poly(tetrahalophenylene sulphide) is prepared by polycondensation of a pentahalothiophenoxide in a basic solvent at 50.degree.-200.degree. C., and proposed it as a process for preparing the same (Japanese patent application Kokai (Laid-Open) No. 36299/1973).
It was also found that a sulphur-containing semi-conductive polymer results from dehalogenation of a poly(tetrahalophenylene sulphide) in the presence or absence of an organic solvent at 150.degree.-500.degree. C., and a Japanese patent was applied for on the process (Japanese patent application Kokai (Laid-Open) No. 42100/1973).
Further, it was found that, when a poly(tetrahalophenylene sulphide) or a sulphur-containing semiconductive polymer obtained by heat-treating the starting material is reacted with an alkali metal, a novel alkali metal-inserted compound with good stability and semiconductivity is produced. A Japanese patent was applied for on the process as such (Japanese patent application Kokai (Laid-Open) No. 46698/1973).
After the foregoing inventions, we found that the alkali metal-inserted compound, although fairly stable in the air as compared with other alkali metal complexes, has a very powerful catalytic activity for the ortho-para-hydrogen conversion. A Japanese patent was applied for on the process, too (Japanese patent application Koaki (Laid-Open) No. 46590/1973).